Attention is directed to article by the inventors and their colleagues entitled "Intracavity loss modulation of Ga-In-As-P diode lasers" 38 Applied Physics Letter 120 (February 1981) and an abstract of the same title at page 2192 of the IEEE Transactions on Electron Devices, Vol. 27, No. 11, (November 1980) describing some aspects of their work. The Applied Physics Letters article and a Sc.D. thesis by D. Z. Tsang, one of the inventors herein, entitled "Intracavity Loss Modulation of Ga-In-As-P Diode Lasers" (catalogued MIT Libraries, Aug. 19, 1981) are hereby incorporated by reference.
Diode lasers are characterized by their ability to lase as a result of an electrical bias applied to a P-N junction. Electron-hole pairs are formed in the junction region which recombine and emit light. Q-switching refers to a method of achieving high pulse rates and high peak power by storing energy in an amplifying medium and then dumping it by rapidly decreasing the intracavity loss to produce nearly simultaneous emissions throughout the medium.
Intracavity loss modulation has been used effectively for Q-switching many gas and solid-state laser systems. Although this technique is capable of producing short optical pulses, high peak powers, and high repetition rates in such systems, it has not been successfully applied to diode lasers. To vary the intracavity loss in diode lasers, the use of electrooptically switched and acousto-optically switched gratings has been proposed. See for example, T. Tsukada and C. L. Tang "Q-switching of Semiconductors" IEEE J. Quantum Electron QE13,37 (1977). However, such devices are not an effective way to produce Q-switching as they do not produce large changes in intracavity losses, in practice.
Intracavity losses in diode lasers have also been modulated by electroabsorption using special growth techniques to produce a tapered active region thickness and varying material composition. See, for example. F. K. Reinhart and R. A. Logan "Monolithically integrated Al-Ga-As double heterostructure optical components" Applied Physics Letters 27 (10), 622 (1974). These devices had limited losses, could not be operated at high modulation rates, and were difficult to fabricate.
There exists a need for a diode laser capable of being Q-switched at high frequencies by an electroabsorptive loss modulator to produce high peak power and serve, for example, as a source for optical communications data bit streams. Preferably, the diode laser should be operable at frequencies up to 2.5 gigahertz or higher and be easily fabricated without special growth techniques.